EP2878151B1 - Équipement d'utilisateur et procédé pour estimer des interférences entre les cellules - Google Patents

Équipement d'utilisateur et procédé pour estimer des interférences entre les cellules Download PDF

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Publication number
EP2878151B1
EP2878151B1 EP12810307.4A EP12810307A EP2878151B1 EP 2878151 B1 EP2878151 B1 EP 2878151B1 EP 12810307 A EP12810307 A EP 12810307A EP 2878151 B1 EP2878151 B1 EP 2878151B1
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Prior art keywords
base station
anchor cell
pmis
ici
cell
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German (de)
English (en)
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EP2878151A1 (fr
Inventor
Lars Thiele
Kai BÖRNER
Martin KURRAS
Johannes DOMMEL
Michael Olbrich
Thomas Haustein
Malte Schellmann
Egon Schulz
Jiayin Zhang
Ni Ma
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Huawei Technologies Co Ltd
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
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Huawei Technologies Co Ltd
Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J11/00—Orthogonal multiplex systems, e.g. using WALSH codes
    • H04J11/0023—Interference mitigation or co-ordination
    • H04J11/005—Interference mitigation or co-ordination of intercell interference
    • H04J11/0053—Interference mitigation or co-ordination of intercell interference using co-ordinated multipoint transmission/reception
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0417—Feedback systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/373—Predicting channel quality or other radio frequency [RF] parameters
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • H04B7/0478—Special codebook structures directed to feedback optimisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B17/00—Monitoring; Testing
    • H04B17/30—Monitoring; Testing of propagation channels
    • H04B17/309—Measuring or estimating channel quality parameters
    • H04B17/345—Interference values
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0636—Feedback format
    • H04B7/0639—Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection

Definitions

  • the invention relates to a user equipment and a method for estimating an inter cell interference in a cellular wireless network comprising cells, wherein each cell comprises a base station.
  • a cellular wireless network can comprise a plurality of cells, wherein each cell comprises a base station. Whereas in some cellular wireless networks the cells are of similar size, other cellular networks can comprise cells of different sizes including macrocells, microcells as well as picocells.
  • MIMO Multiple Input-Multiple Output
  • MIMO Multiple Input-Multiple Output
  • a MIMO system there are more than one transmit antenna to send a signal on the same frequency and more than one receive antenna.
  • traditional cellular networks generally provide a best service under line of sight conditions, the MIMO system is most sufficient under rich scattering conditions where signals bounce around the environment. Under rich scattering conditions signals from different antennas take multiple paths to reach the UE at different times.
  • the MIMO system uses a technique, the so-called spatial multiplexing.
  • spatial multiplexing By use of spatial multiplexing the data rate can be increased. To do this, the data is divided into separate streams, wherein the data streams are transmitted independently via separate antennas. In spatial multiplexing each antenna has a different data stream to multiple receiving antennas. These data streams are then reconstructed separately by the UE. In spatial multiplexing, although multiple data streams are transmitted, the total power of the transmission remains the same.
  • each data stream contains a lower SNR than would be possible with a single data stream.
  • rank refers to the number of data streams transmitted over the same kind of frequency resource, corresponding to the number of layers.
  • Fig.1 shows a diagram for illustrating spatial multiplexing as employed in a conventional wireless cellular network.
  • Spatial multiplexing works by creating separate data streams on multiple antennas. With spatial multiplexing, independent data streams can be transmitted simultaneously on the same frequency resource by mapping them to so called spatial layers. The number of spatial layers is the same as the rank, R, of the precoding matrix used for data transmissions.
  • data arriving from a higher level process comprises codewords. Each codeword is then mapped onto one or more layers. Each layer is then mapped onto one or more antennas using a precoding matrix.
  • a cellular network can operate in an open or closed loop. In an open loop operation the base station receives minimal information.
  • the UE analyses the channel conditions of each transmitting antenna including the multi-path conditions.
  • the UE provides an RI as well as a PMI, which indicates the optimum PM for the current channel conditions.
  • the UE can provide a CQI given the RI and the PMI. This allows the base station to quickly and effectively adapt the transmission to channel conditions. Closed loop operations are particularly relevant for spatial multiplexing, where the MIMO system offers the greatest throughput gains.
  • each codeword is then mapped onto one or more layers.
  • Each layer is then mapped onto one or more antennas using a PM.
  • This PM can be taken from a CB, wherein a predetermined set of PMs is stored.
  • Each PM comprises a corresponding PMI.
  • the MIMO system can be implemented for instance in an LTE network.
  • an SINR of a UE depends on both signal power and ICI.
  • the prediction or estimation of ICI is an important factor to improve the CQI precision and thus link adaption.
  • link adaption is always affected by a delay of the CQI feedback.
  • the effect of Doppler shift may be alleviated by channel prediction methods.
  • each UE provides feedback on the PMI which can be wideband, and CQI which can be wideband or provided per each subband.
  • a base station scheduler decides to provide resources in the time/frequency/space for a set of UEs in the respective cell of the wireless network.
  • Each base station can select its UEs according to the following predetermined scheduling policies on the basis of the received feedback.
  • the main reasons for performance loss are related to a feedback delay. Channel conditions may change in the meantime and therefore scheduling decisions may not be optimal any longer.
  • This cell-dependent CB selection for a PM can be used for a precoding downlink transmission.
  • Each cell of the wireless network may optimize the downlink precoding configuration for its own UEs. Hence, after reconfiguration, the ICI which is caused by neighbouring cells can significantly change its spatial structure. Thus, the downlink interference observed at the UE side may be highly dynamic.
  • the experienced multicell or ICI strongly depends on the PMs selected by the neighbouring base stations.
  • the ICI experienced by UE in the neighbouring cells may significantly change.
  • Precoding and transmission configurations in these cells of the wireless network which were based on the interference situation generated by the previous selection of PMs and precoding weights in the cell, do then no longer match the actual interference situation and a performance degradation can be observed.
  • US2010002643 (A1 ) discloses a method for operating a Mobile Station in a Multiple Input Multiple Output wireless communication system.
  • the method includes measuring channel quality for a serving Base Station, if the channel quality is less than a threshold, measuring interference power from one or more neighbor Base Stations, determining a Precoding Matrix Index and a priority metric for each neighbor Base Station, and feeding back at least one of the PMI, a PMI type indicator, the priority metric, and the channel quality to the serving Base Station.
  • WO2011123460 (A1 ) discloses a system and method of coordinating scheduling in a wireless communication system.
  • Cells receive information regarding one or more precoding matrices from user equipments.
  • the information may include a request from an user equipment that the cell not use a particular precoding matrix for communications.
  • the cell may determine whether restricting usage of the precoding matrix for communication improves overall communication in the wireless communication system by performing pair-wise comparisons of utility based on usage and restriction of the precoding matrix.
  • the cell may further resolve conflicts that arise between several cells based on the granting of restriction of the precoding matrix.
  • WO2010104343 discloses a multiple antenna system including a mobile station and a base station are operable to perform a method for transmitting control information for interference mitigation.
  • a Mobile Station can transmit control information for interference mitigation.
  • the Mobile Station determines a first Precoding Matrix Index (PMI) and a second PMI for interference from an adjacent Base Station. Based on a correlation level from correlation values between one of the first PMI and second PMI and the remaining PMIs in the codebook, the Mobile Station determines a level of a subset of PMIs, and feeds back information indicating the correlation level.
  • PMI Precoding Matrix Index
  • WO2010002230 discloses a method for avoiding inter-cell interference in a closed-loop multiple-input multiple-output system using a plurality of codebooks.
  • a base station of a serving cell transmits information about codebooks used in an interfering cell among the plurality of codebooks to a mobile station. The transmission of the information may be made at the request of the mobile station. Alternatively, the mobile station may directly measure information about codebooks used in the interfering cell among the plurality of codebooks.
  • the mobile station measures restricted precoding matrix indexes (PMIs) or requested PMIs based on the codebook information. The measured PMIs are transmitted to the interfering cell and are used to restrict the use of a PMI in the interfering cell.
  • PMIs restricted precoding matrix indexes
  • WO2009084905 discloses a method for reducing inter-cell interference and a method for transmitting a signal by a collaborative MIMO scheme, in a communication system having a multi-cell environment.
  • An example of a method for transmitting, by a mobile station, precoding information in a collaborative MIMO communication system includes determining a precoding matrix set including precoding matrices of one more base stations including a serving base station, based on signal strength of the serving base station, and transmitting information about the precoding matrix set to the serving base station.
  • a mobile station in an edge of a cell performs a collaborative MIMO mode or inter-cell interference mitigation mode using the information about the precoding matrix set collaboratively with neighboring base stations.
  • WO2011018031 discloses a method for wireless communication that includes receiving cell information for a cluster of cells to be coordinated.
  • a first cluster scheduling order used for the cluster of cells is retrieved.
  • the first cluster scheduling order represents a sequence in which the cluster of cells were scheduled in a previous schedule.
  • a second cluster scheduling order is generated.
  • the second cluster scheduling order determines a sequence in which the cluster of cells are scheduled in an upcoming schedule.
  • the second cluster scheduling order is decided based on the first cluster scheduling order and/or the cell information.
  • the second cluster scheduling order is transmitted to the cluster of cells.
  • US2010002643 discloses a method for operating a Mobile Station in a Multiple Input Multiple Output wireless communication system.
  • the method includes measuring channel quality for a serving Base Station (BS), if the channel quality is less than a threshold, measuring interference power from one or more neighbor BSs, determining a Precoding Matrix Index (PMI) and a priority metric for each neighbor BS, and feeding back at least one of the PMI, a PMI type indicator, the priority metric, and the channel quality to the serving BS.
  • BS serving Base Station
  • PMI Precoding Matrix Index
  • a UE registered with an anchor cell base station of an anchor cell of a cellular wireless network wherein the UE comprises a determination unit being adapted to predict an ICI at the UE, caused by base stations of neighbouring cells, depending on PMIs of PMs, the PMIs being exchanged between the anchor cell base station of the anchor cell and the base stations of the neighbouring cells.
  • the prediction of the ICI from a neighbouring base station can be performed by multiplying the PMI used by the base station with a channel function between the UE and the base station, that has been measured by the UE.
  • the UE comprises an interface for receiving the PMIs from the anchor cell base station.
  • the ICI predicted by the determination unit of the UE is advertised by the UE to its anchor cell base station.
  • the ICI predicted by the UE and advertised by the UE to its anchor cell base station is evaluated by the anchor cell base station, to select a PMI of a matching PM.
  • the PMIs of the PMs exchanged between the anchor cell base station of the anchor cell and the base stations of the neighbouring cells indicate PMIs to be used by a base station in a predetermined number of future subframes.
  • the UE is adapted to predict the ICI at the UE on the basis of the exchanged PMIs and channel transfer functions of physical channels between the UE and the base stations of all neighbouring cells, measured by the UE.
  • the PMIs indicate an optimum PM used by the base station for a current channel condition between the anchor cell base station and the UE.
  • the exchanged PMIs are supplied as ACI by the anchor cell base station to the UE via a PDCCH.
  • the ACI comprises a timestamp indicating how long the ACI is valid.
  • the exchanged PMIs form a PM indication sequence comprising a fixed pattern of specific PMIs or a generic pattern of arbitrary PMIs.
  • the predicted ICI received by the anchor cell base station from the UE is evaluated by the anchor cell base station, to select a PMI of a matching PM, wherein by selecting the respective PMI an SINR of a reception signal received by the registered UE in the anchor cell is maximized.
  • a method for estimating an ICI, in a cellular wireless network comprising cells comprising cells, wherein each cell comprises a base station, the method comprising the steps of:
  • the prediction of the ICI from a neighbouring base station can be performed by multiplying the PMI used by the base station with a channel function between the UE and the base station, that has been measured by the UE.
  • the UE comprises an interface for receiving the PMIs from the anchor cell base station.
  • the ICI predicted by the determination unit of the UE is advertised by the UE to its anchor cell base station.
  • the ICI predicted by the UE and advertised by the UE to its anchor cell base station is evaluated by the anchor cell base station, to select a PMI of a matching PM.
  • the PMIs of the PMs exchanged between the anchor cell base station of the anchor cell and the base stations of the neighbouring cells indicate PMIs to be used by a base station in a predetermined number of future subframes.
  • the UE predicts the ICI at the UE on the basis of the exchanged PMIs and channel transfer functions of physical channels between the UE and the base stations of all neighbouring cells, measured by the UE.
  • the PMIs indicate an optimum PM used by the base station for a current channel condition between the anchor cell base station and the UE.
  • the exchanged PMIs are supplied as ACI by the anchor cell base station to the UE via a PDCCH.
  • the ACI comprises a timestamp indicating how long the ACI is valid.
  • the exchanged PMIs form a PM indication sequence comprising a fixed pattern of specific PMIs or a generic pattern of arbitrary PMIs.
  • the predicted ICI received by the anchor cell base station from the UE is evaluated by the anchor cell base station, to select a PMI of a matching PM, wherein by selecting the respective PMI an SINR of a reception signal received by the registered UE in the anchor cell is maximized.
  • a base station of an anchor cell (2-0) of a cellular wireless network comprising an evaluation unit being adapted to evaluate an ICI, wherein the ICI is predicted by a UE registered with the base station, caused by base stations of neighbouring cells, depending on PMIs of PMs, the PMIs being exchanged between the base station of the anchor cell and the base stations of the neighbouring cells.
  • an SINR of a reception signal received by the UE in the anchor cell in view of the predicted ICI is maximized by selecting the respective PMI.
  • a wireless cellular network comprising cells, each cell comprising a base station, wherein PMIs of PMs are exchanged between base stations of neighbouring cells, and a UE registered with an anchor cell base station is adapted to predict an ICI at the UE, caused by the base stations of the neighbouring cells, depending on the exchanged PMIs.
  • the wireless cellular network is a wireless multi-antenna network comprising a CAS or a DAS.
  • the aspects of the present invention allow for a reliable prediction of SINR conditions at the UE, which improves the precision of CQI values used for link adaption. Consequently, a higher throughput on link level as well as on system level can be achieved, thus improving the achievable overall spectral efficiency in the cellular wireless network.
  • Fig. 2 shows a schematic diagram of a possible implementation of a cellular wireless network 1 according to an embodiment of the present invention.
  • the cellular wireless network 1 comprises a plurality of cells 2-1, each cell comprising a base station 3-i.
  • cells 2-1 to 2-7 are shown each having a base station 3-1 to 3-7.
  • Fig. 2 shows a cluster of cells 2-i, wherein an anchor cell 2-0 is surrounded by neighbouring cells 2-1 to 2-6.
  • the cellular wireless network 1 is a homogeneous network comprising cells 2-i of similar size.
  • the cellular wireless network 1 can also be a heterogeneous network comprising cells of different types and size such as macrocells, microcells or even picocells. Accordingly, the cell structure of the cells 2-i of the cellular wireless network 1 as shown in Fig. 2 is exemplary only and the structure of the cellular wireless network 1 may vary comprising cells of different cells and types.
  • the base stations 3-i of the cellular wireless network 1 can be connected to each other by means of a backhaul network providing network interfaces between the base stations.
  • Each base station 3-i can comprise a BBU which is connected to BBUs of neighbouring cells.
  • a BBU of a cell 2-i can be connected to one or several RRUs.
  • Each RRU can be provided directly at the location of the base station 3-i or can be at a remote location within the cell and connected to the base station via a link.
  • Each RRU can comprise several antennas which are adapted to transmit and receive signals to/from a UE 4 registered with the base station 3-i of the respective cell 2-i.
  • the UE 4 can be any kind of mobile terminal such as a mobile phone.
  • the cellular system can make use of RRUs in a DAS, to provide a more uniform coverage, reduced outage and higher throughputs especially in indoor locations.
  • the DAS can be combined with MIMO communications concepts by treating the RRUs at a distributed antenna array and/or equipping the RRUs with multiple antennas.
  • the base stations 3-i shown in the cellular wireless network 1 in Fig. 2 can be formed by eNodeBs of an LTE wireless network.
  • the base stations 3-i can be connected to each other via an X2 interface.
  • the wireless cellular network shown in Fig. 2 can also be formed by a WIMAX network or a UMTS network.
  • each cell 2-i has a base station 3-i, wherein PMIs of PMs are exchanged between the base station 3-i of neighbouring cells.
  • the exchange of PMIs is performed via a backhaul network connecting the base stations 3-i with each other.
  • the UE 4 registered with the anchor cell base station 3-0 is adapted to predict an ICI at the UE caused by the base stations of the neighbouring cells 2-1 to 2-6 depending on the exchanged PMI.
  • the number of neighbouring cells of the anchor cell 2-0 can vary. In the exemplary embodiment shown in Fig. 2 all neighbouring cells 2-1 to 2-6 are located in a first ring around the anchor cell 2-0.
  • the neighbouring cells can also be located in a further ring around the anchor cell 2-0.
  • the exchanged current PMIs are provided for selecting a PM from a CB.
  • the PMIs can be valid for a specified number of future subframes. This exchange of PMIs can easily be done in case of co-located antennas or a CAS. Further, the information exchange can be performed between DASs connected to the same BBU.
  • Fig. 3 shows a flow chart of a possible implementation of a method for estimating an ICI in a cellular wireless network 1, according to an embodiment of the present invention.
  • the method for estimating an ICI in a cellular wireless network comprising cells, each cell having a base station 3-i, comprises two main steps.
  • a first step S1 the PMIs of PMs are exchanged between an anchor cell base station 3-0 and base stations 3-i of neighbouring cells 2-i.
  • the PMIs of PMs are exchanged between the anchor cell base station 3-0 and the base stations of the neighbouring cells 2-1 to 2-6.
  • the UE 4 registered with the anchor cell base station 3-0 of the anchor cell 2-0 predicts an ICI at the UE 4 caused by the base stations 3-1 to 3-6 of the neighbouring cells 2-1 to 2-6, depending on the PMIs exchanged in step S1 and supplied by the anchor cell base station 3-0 to the registered UE 4 via a downlink.
  • the ICI from a neighbouring base station is performed by multiplying the PMI used by the base station with the channel function between the UE and the base station, that has been measured by the UE.
  • the predicted ICI predicted in step S2 can be advertised by the UE 4 to the anchor cell base station 3-0 to which it is registered.
  • the ICI predicted by the registered UE 4 and advertised by the UE 4 to its anchor cell base station 3-0 can be evaluated in a possible implementation form by the anchor cell base station 3-0, to select a PMI of a matching PM, wherein by selecting the respective PMI a signal quality of a reception signal received by the registered UE 4 is maximized.
  • the PMIs of the PMs exchanged between the anchor cell base station 3-0 and the base stations 3-i of the neighbouring cells 2-i can indicate PMs to be used by a base station in a predetermined number of future subframes.
  • the registered UE 4 predicts in step S2 the ICI at the UE 4 on the basis of the exchanged PMIs and on the basis of channel transfer functions of physical channels between the registered UE 4 and the base stations of all neighbouring cells measured by the registered UE 4.
  • the PMIs can indicate an optimum PM used by the base station for a current channel condition between all base stations and the registered UE 4.
  • the exchanged PMIs exchanged in step S1 are supplied as ACI by the anchor cell base station 3-0 to the registered UE 4 via a predetermined channel such as the PDCCH. Via the PDCCH each cell provides ACI for a set of neighbouring cells to its assigned and registered UEs 4.
  • the ACI can include a cell-specific selection of active PMIs for precoded downlink services for a set of neighbouring base stations or eNodeBs.
  • the ACI can comprise in a possible implementation form a timestamp indicating how long the ACI is valid. A timestamp can be an index which is defined either per cell or as a common value for all cells inside the cell cluster as shown in Fig. 2 .
  • the exchanged PMIs can form a PM indication sequence. This PM indication sequence can comprise a fixed pattern of specific PMIs or a generic pattern of arbitrary PMIs as also illustrated in Fig. 6 .
  • the ICI received by the anchor cell base station 3-0 from the registered UE 4 can be evaluated by the anchor cell base station 3-0 to select a PMI of a matching PM, to maximize a SINR of a reception signal received by the registered UE 4 in the anchor cell 2-0 in view of the predicted ICI.
  • the prediction or estimation method allows flexibility to choose CBs from PMs in frequency and time.
  • the interaction delay is the time duration of a selected PMI configuration at a given base station. As a result the ICI to a given base station 3-i is kept predictable for a time duration equivalent to the interaction delay.
  • the signalization delay is the time duration required for exchanging active PMI information between neighbouring base stations and the additional time duration for a downlink signalization to the registered UEs.
  • the time duration required for exchanging the active PMI information depends on the configuration of the backhaul network connecting the base stations 3-i with each other. Additional time duration for downlink signalization to the UEs is cell-specific and can be optimized to accommodate the registered UE 4 of the respective cell 2-i.
  • a stabilized ICI in a cellular wireless network 1 comprising the steps as shown in the flow chart of Fig. 4 .
  • the ICI in a cellular wireless network is not only predicted but also stabilized.
  • the method for providing a stabilized ICI in a cellular wireless network 1 comprises steps S1 and S2 of the method for estimating an ICI at a UE 4 registered with an anchor cell base station 3-0, according to an embodiment of the present invention, and a further main step S3.
  • step S3 the predicted ICI at the UE 4 is advertised by the registered UE 4 to its anchor cell base station 3-0.
  • the advertised predicted ICI of the UE 4 is evaluated to select a PMI of a matching PM, to maximize the signal quality of a reception signal received by the registered UE 4.
  • Fig. 5 shows a timing diagram of a possible exemplary signaling protocol for exchange of PMIs between base stations of the wireless cellular network 1 and the UE 4.
  • a first base station 3-i provides another base station 3-j via the backhaul connection or interface with PMIs of PMs.
  • this PMI information is sent by the first base station 3-i to its registered UE 4 as shown in Fig. 5 .
  • the other base station 3-j provides the first base station 3-i also with PMI information of the used PMs.
  • This received PMI information is then supplied by the first base station 3-i to its registered UE 4, as shown in Fig. 5 .
  • the registered UE 4 registered with the first base station 3-i has information about the PMIs used by its anchor cell base station 3-i and the PMIs of the PMs used by the base station 3-j of its neighbouring cell.
  • the UE 4 registered with the anchor cell base station 3-i predicts the ICI caused by the base stations 3-j of all neighbouring cells 2-i, depending on the PMIs transmitted by the anchor cell base station 3-i downlink to the registered UE 4.
  • FIG. 5 shows the signalization delay which is the time required for exchanging the active PMI information between the neighbouring base stations 3-i and 3-j and the additional time duration for downlink signalization to the UE 4.
  • the interaction delay shown in the diagram of Fig. 5 is the time duration of a selected PMI configuration at any base station 3-i, 3-j.
  • the interaction delay period is the same for both base stations 3-i, 3-j, as shown in Fig. 5 , but shifted with respect to each other.
  • the maximum signalling overhead depends on the amount of ACI provided per cell. Moreover, the maximum signalling overhead comprises the transport of cell-IDs of the respective cells when exchanging the ACI. Moreover, the signalling overhead comprises a start time for the respective base station to use the exchanged PMIs and the duration time indicating how long the respective PMIs can be used for precoding. As can be seen in Fig. 5 , there exists a trade off between interaction delay and PM adaption. A PM adaption is required to follow changes in the positions of the UE 4. For instance, the UE 4 might move for a predetermined number of wavelengths within the cell 2. Moreover, the PM adaption has to take into account the existence of new registered UEs 4 within the cells.
  • the signalization delay as well as the interaction delay are preconfigured or adaptable depending on the required service applications provided by the cellular wireless network 1 to the UEs 4.
  • the PMI adaption can exhibit high dynamics at equivalent amounts of feedback overhead due to signalization of predefined PM sequences.
  • the exchanged PMIs can form a PM indication sequence.
  • This PM indication sequence can comprise a fixed pattern of specific PMIs, as shown in Fig. 6 above, or a generic pattern of arbitrary PMIs as shown in Fig. 6 below.
  • a first PM indication sequence with a fixed pattern can, for instance, comprise the PMIs PMI1, PMI2, PMI1 and a second PM indication sequence with a fixed pattern can comprise the PMIs PMI4, PMI2, PMI3 as illustrated in Fig. 6 .
  • the PM indication sequence can also comprise a generic pattern of arbitrary PMIs.
  • a first possible example for a generic pattern of arbitrary PMIs is the PM indication sequence PMIa, PMIa, PMIb.
  • a further example for a PM indication sequence comprising a generic pattern of arbitrary PMIs is the sequence PMIb, PMIa, PMIa.
  • PMIa can be instantiated by PMI1 and PMIb can be instantiated by PMI3.
  • the first PM indication sequence becomes after specification PMI1, PMI1, PMI3.
  • this generic sequence can also be specified in that the generic PMIa is specified to become PMI2 and the other generic PMIb becomes a specific PMI4.
  • the first generic PM indicator sequence becomes PMI2, PMI2, PMI4.
  • the neighbouring cells 2-i can exchange the current PM selection which is valid for a specified number of future subframes. This information exchange can easily be done in case of co-located antennas, e.g. sectors of the same site or between DASs connected to the same BBU.
  • Cells 2-i belonging to a cell cluster for a wireless cellular network 1 can coordinate their PM selection within a CB over an available frequency band according to a predefined sequence pattern. This sequence can use specific PMIs in a certain time/frequency pattern, as illustrated in Fig. 6 .
  • a definition of a generic time/frequency sequence is performed by using arbitrary PMIs, as shown in the lower part of Fig. 6 .
  • each cell 2-i can provide the ACI sequence to a set of neighbouring cells 2-i inside a cluster of cells 2-i.
  • the selection of the active CB information ACI sequence which defines the order of the PMIs, is performed in time/frequency domain.
  • a cluster of multiple base stations can, according to a possible implementation form, agree on using a common PM indication sequence.
  • the PM indication sequences are defined in advance and are known to the base stations 3-i as well as to the UE 4.
  • the exchange of PM indicator sequences can be done on longer time scales such as on a radio frame basis.
  • a further advantage of this approach lies in the fact that it allows for further reduction of the amount of information or data exchange, which is required between the different neighbouring base stations 3-i of the wireless cellular network 1, as shown for example in Fig. 2 .
  • the PM indicator sequences can be adjusted according to relative frequencies of PMI selections provided in the user specific PMI feedback. For instance, 20% of the UEs 4-i can report a PMI1, whereas the remaining 80% of the UEs within the cell report another PMI2. Depending on the relative choice of the PMI selections by the UEs the PM indicator sequences can be adjusted.
  • the required control signal overhead comprises the sequence of PMIs per cell 2-i as well as an identifier ID of the respective cell 2-i and a corresponding time-offset.
  • FIGS. 7A, 7B show schematic diagrams for illustrating the operation of the method according to an embodiment of the present invention.
  • the cells 2-i of a wireless cellular network 1 are illustrated, wherein different cells are located around an anchor cell 2-0, shown in Figs. 7A and 7B in the center.
  • the anchor cell 2-0 is surrounded by a first ring of cells which in turn is surrounded by a second ring of cells.
  • an ICI predicted by the UE registered to the base station 3-0 of the anchor cell 2-0 is performed not only depending on the PMIs exchanged between the anchor cell base station 3-0 of the anchor cell 2-0 and the base stations 3-i of the neighbouring cells 2-i in the first ring, but also depending on the exchanged PMIs used by the base stations 3-i in the second ring around the anchor cell 2-0.
  • FIGs 8A, 8B illustrate the situation in a conventional wireless cellular network in comparison to a situation when using a method for stabilizing an ICI in a wireless cellular network 1 according to the present invention.
  • Fig. 8A represents the situation where cells in a conventional wireless cellular network adapt their downlink precoding matrices or precoders independently. Consequently, the SINR conditions are only imprecisely estimated (E) when compared to perfect (P), as illustrated in Fig. 8A .
  • This effect of changing precoders on the variance of the SINR is commonly known as a flashlight effect which can be even more severe in a DAS. The effect of changing interference from neighbouring cells is called the flashlight effect.
  • the method for estimating an ICI in a cellular wireless network 1 according to the present invention uses a standard CQI and PMI feedback of the users, but with a certain degree of coordination of the scheduling decisions taken by the base stations in the neighbouring cells.
  • Fig. 8B shows the application of a coordination scheme for neighbouring cells as employed by the method according to an embodiment of the present invention.
  • the SINR conditions can be estimated with high precision by the method for estimating an ICI according to an embodiment of the present invention.
  • the remaining degradation visible in Fig. 8B mainly depends on Doppler shifts which can be handled separately by channel prediction.
  • a potential quantitative gain in data throughput can be achieved when SINR can be predicted using a method for estimating an ICI in a cellular wireless network 1 according to an embodiment of the present invention.
  • This potential quantitative gain in throughput is achieved thanks to a coordination between the base stations 3-i compared to a conventional wireless cellular network where no coordination in this respect is provided.
  • each CB entry or the PM in neighbouring cells is randomly selected following a uniform distribution.
  • the PMs or precoders are selected by a scheduling entity provided in each cell of the wireless cellular network. Consequently, its selection can behave random-like from the perspective of the UE in the different cells.
  • each CB entry or PM in each cell is active for a certain number of subframes, for example for two subframes. This can be the case due to scheduling decisions when selecting the same UE to be served for future subframes or when selecting a second UE for future subframes but this second UE has reported the same PMI as the first UE.
  • Each subframe can have a predetermined number of symbols such as OFDM symbols. A predetermined number of symbols are transmitted during a transmission time interval, TTI, corresponding to one subframe.
  • Fig. 10 shows a schematic diagram of a wireless cellular network 1 with a first and a second ring of neighbouring cells around an anchor cell 2-0.
  • Strong interference from the first ring of neighbouring cells 2-i causes the most of the SINR degradation at a UE registered with the anchor cell base station 3-0 of the anchor cell 2-0.
  • predicting the multi cell interference or ICI provides significant gains. This prediction is performed by the method for estimating an ICI in a cellular wireless network 1 according to an embodiment of the present invention.
  • Fig. 11 shows a diagram with cumulative probability distribution functions, CDF, which represent the SINR degradation between succeeding frames.
  • CDF cumulative probability distribution functions
  • the SINR degradation is the difference between the SINR estimated at the UE during frame n and the measured SINR during the succeeding frame n+1.
  • the degradation is mainly caused by a change of PMIs in neighbouring cells, and since PMIs may change after frames only, the SINR degradation will be observed between succeeding frames.
  • the first curve I shows the case where no coordination between the base stations 3-i of the wireless cellular network 1 takes place.
  • the second curve II is almost identical with the third curve III, wherein the second curve II shows the case where PMIs are exchanged between the anchor cell base station 3-0 and the base stations of the direct neighbouring cells in the first ring of the wireless cellular network 1, whereas the curve III shows the case where the PMIs are not only exchanged between the anchor cell base station 3-0 of the anchor cell 2-0 and the base stations of the immediately neighbouring cells, but also with the base stations located in the second ring around the anchor cell 2-0. Accordingly, in most applications the exchanging of PMIs between the anchor cell base station 3-0 of the anchor cell 2-0 and the base stations of the direct neighboring cells of the first ring around the anchor cell 2-0 is sufficient as illustrated by Fig. 11 .
  • Fig. 12 shows another integrated probability distribution function, CDF, for the achievable throughput of a sector or base station of the anchor cell.
  • the first curve I shows again the case where no coordination between the base stations takes place such as in a conventional wireless cellular network.
  • the almost identical curves II, III show the cases where sequence based coordination or exchange of PMIs takes place among all cells (curve III) of the first and second ring and where a sequence based coordination takes place only among direct neighbouring cells, i.e. between the anchor cell 2-0 and the cells of the first ring (curve II). Again it can be seen that the gains from predicting interference signals caused by base stations of the second ring are relatively small.
  • Fig. 12 shows another integrated probability distribution function, CDF, for the achievable throughput of a sector or base station of the anchor cell.
  • the first curve I shows again the case where no coordination between the base stations takes place such as in a conventional wireless cellular network.
  • the almost identical curves II, III show the cases where sequence based coordination or exchange of PM
  • Curve III shows the situation where a complete knowledge of the CB and PM configurations in all neighbouring cells is provided.
  • the system throughput degrades by 20% at the median value due to the flashlight effect.
  • sequence based PM coordination which considers all cells in the first tier or ring, it is possible to mitigate almost the complete degradation with respect to the median value of the ideal feedback case, translating to a gain of approximately 25%.
  • an almost static behaviour of the ICI can be achieved by a coordinated selection of PM configurations within a cluster of neighbouring cells or by a regular pattern of PM configurations.
  • the almost static ICI provides stable CQI measurements of the UE that do not change for a specific time duration, thus enabling a significant throughput gain for single UEs as well as for the entire system.
  • the coordination of PM selection can take place within a set of neighbouring cells within the wireless network 1. This coordination can use specific coordination schemes. Regular patterns of PM configurations can be used. Different patterns for a systematic switching between PM configuration can be employed. A scheme for pattern adaption can depend on the current (global) user demands.
  • a central control entity or unit can choose the CBs and the precoding matrices of these CBs for neighbouring cells such that an interference shaping can be applied to improve the CQI conditions.
  • an interference shaping can be applied to improve the CQI conditions.
  • reliable ICI estimations can be performed at the UE.
  • a cluster of neighbouring cells 2-i can be defined.
  • the definition of the set of neighbouring cells within the cluster constituting the area of coordinated base stations 3-i can be defined without backhaul constraints or with backhaul constraints.
  • the definition of the set of neighbouring cells within a cell cluster of a wireless cellular network 1 can be performed without considering backhaul constraints of the backhaul network connecting the base stations 3-i so that the information for CB and PM coordination is exchanged within all cells in the vicinity of the anchor cell 2-0, i.e. the cell of interest in the middle of the cluster, as shown in Fig. 2 .
  • the selection or definition of the set of neighbouring cells can also take into account backhaul constraints of the backhaul network or interface between the base stations. For example, based on the UE feedback, UEs are assumed to report on less than their six strongest interfering cells. Thus, each base station can evaluate this feedback of the UE and establish an inter-base station connection to neighbouring cells of highest relevance.
  • a set of cells forming a cell cluster can be defined by the network operator and can remain constant for a longer period.
  • the determination unit of the UE can be a processor being adapted to predict an ICI at the UE, caused by the base stations of the neighbouring cells, depending on PMIs of PMs, the PMIS being exchanged between the anchor cell base station of the anchor cell and the base stations of the neighbouring cells.
  • a base station of a cellular wireless network comprises an evaluation unit or a processor, which is adapted to evaluate an ICI predicted by a UE registered with the base station.
  • the method and apparatus according to the different embodiments of the present invention allow a reliable prediction of changes in the selection of PMIs in base stations of adjacent cells based on predefined time frames.
  • an ICI situation is predictable in each cell of the wireless cellular network.
  • the estimation of the ICI in each cell allows a reliable configuration of precoding and transmission configurations for the current anchor cell to which the UE is registered.
  • the CQIs are used to adapt to small-scale fading in scheduling processes. Therefore, the CQIs are provided on a subframe basis. Additional PMIs are provided by the UE in order to indicate which beam index is desired and for which index CQI feedback is provided.
  • the PMIs can be selected based on a geo-location of the specific UE so that different PMIs of the UE represent a spatial user distribution.
  • the positions of UEs within a cell can change so that a corresponding adaption of the CBs and/or PMIs of the PMs within the CBs and a certain degree of coordination between the neighbouring base stations can be performed.
  • the CQI feedback on the UE can still be provided on different time scales. Accordingly, in a possible implementation a different time scale for the coordination of the PMIs and the CQI information can be used.
  • the method for estimating an ICI in a cellular wireless network according to an embodiment of the present invention and the method for providing a stabilized ICI in a cellular wireless network according to a further embodiment of the present invention can be performed by computer programs executed by a execution unit or processor of the base station and/or UEs within the wireless network.
  • the prediction of the ICI can be performed by the determination unit of the UE.
  • This determination unit can be a microprocessor performing the prediction by executing corresponding instructions of a computer program.
  • the computer program may be stored in a computer readable storage medium, such as e.g. a ROM, a magnetic disk or an optical disk.
  • the exchange of the PMIs between the anchor cell base station and the base stations of the neighbouring cells can be performed by a predetermined protocol.

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Claims (14)

  1. Équipement d'utilisateur (UE) (4) enregistré auprès d'une station de base de cellule d'ancrage (3-0) d'une cellule d'ancrage (2-0) d'un réseau cellulaire sans fil (1), l'équipement d'utilisateur (4) comprenant un module de détermination qui est conçu pour prédire une interférence intercellulaire (ICI) au niveau de l'équipement d'utilisateur (4), provoquée par des stations de base (3-1 à 3-6) de cellules voisines (2-1 à 2-6), en fonction d'indicateurs de matrice de précodage (PMI) de matrices de précodage (PM), les indicateurs PMI étant fournis par la station de base de cellule d'ancrage (3-0) de la cellule d'ancrage (2-0) à l'équipement d'utilisateur (4) et étant échangés entre la station de base de cellule d'ancrage (3-0) de la cellule d'ancrage (2-0) et les stations de base (3-1 à 3-6) des cellules voisines (2-1 à 2-6).
  2. Équipement d'utilisateur (4) selon la revendication 1, dans lequel l'équipement d'utilisateur (4) comprend une interface pour recevoir les indicateurs PMI en provenance de la station de base de cellule d'ancrage (3-0).
  3. Équipement d'utilisateur (4) selon la revendication 1 ou 2, dans lequel l'interférence ICI prédite par l'unité de détermination de l'équipement d'utilisateur (4) est annoncée par l'équipement d'utilisateur (4) à sa station de base de cellule d'ancrage (3-0).
  4. Équipement d'utilisateur (4) selon la revendication 3, dans lequel l'interférence ICI prédite et annoncée par l'équipement d'utilisateur (4) à sa station de base de cellule d'ancrage (3-0) est évaluée par la station de base de cellule d'ancrage (3-0) pour sélectionner un indicateur PMI d'une matrice PM assortie.
  5. Équipement d'utilisateur (4) selon l'une des revendications 1 à 4, dans lequel les indicateurs PMI des matrices PM échangés entre la station de base de cellule d'ancrage (3-0) de la cellule d'ancrage (2-0) et les stations base (3-1 à 3-6) des cellules voisines (2-1 à 2-6) indiquent des indicateurs PMI qui doivent être utilisés par une station de base (3-i) dans un nombre prédéterminé de futures sous-trames.
  6. Équipement d'utilisateur (4) selon l'une des revendications 1 à 5, dans lequel l'équipement d'utilisateur (4) est conçu pour prédire l'interférence ICI au niveau de l'équipement d'utilisateur (4) sur la base des indicateurs PMI échangés et de fonctions de transfert de canal de canaux physiques entre l'équipement d'utilisateur (4) et les stations de base (3-1 à 3-6) de toutes les cellules voisines (2-1 à 2-6), mesurée par l'équipement d'utilisateur (4).
  7. Équipement d'utilisateur (4) selon l'une des revendications 1 à 6, dans lequel les indicateurs PMI indiquent une matrice PM optimale utilisée par la station de base pour une condition de canal actuelle entre la station de base de cellule d'ancrage (3-0) et l'équipement d'utilisateur (4).
  8. Équipement d'utilisateur (4) selon l'une des revendications 1 à 7, dans lequel les indicateurs PMI échangés sont fournis sous la forme d'informations de livre de codes actives (ACI) par la station de base de cellule d'ancrage (3-0) à l'équipement d'utilisateur (4) par le biais d'un canal de commande de liaison descendante physique (PDCCH).
  9. Équipement d'utilisateur (4) selon la revendication 8, dans lequel les informations ACI comportent une estampille temporelle indiquant la durée pendant laquelle les informations ACI sont valides.
  10. Équipement d'utilisateur (4) selon l'une des revendications 1 à 9, dans lequel les indicateurs PMI échangés forment une séquence d'indications de matrice PM comprenant un motif fixe d'indicateurs PMI spécifiques ou un motif générique d'indicateurs PMI arbitraires.
  11. Équipement d'utilisateur (4) selon l'une des revendications 1 à 10, dans lequel l'interférence Ici prédite reçue par la station de base de cellule d'ancrage (3-0) en provenance de l'équipement d'utilisateur (4) est évaluée par la station de base de cellule d'ancrage (3-0) pour sélectionner un indicateur PMI d'une matrice PM assortie, dans lequel en sélectionnant l'indicateur PMI, un rapport signal sur interférence plus bruit (SINR) d'un signal de réception reçu par l'équipement d'utilisateur (4) dans la cellule d'ancrage (2-0) est maximisé.
  12. Procédé pour estimer une interférence intercellulaire (ICI) au niveau d'un équipement d'utilisateur (4), provoquée par des stations de base (3-1 à 3-6) de cellules voisines (2-1 à 2-6), dans un réseau cellulaire sans fil (1) comprenant des cellules (2-i), dans lequel chaque cellule comprend une station de base (3-i), le procédé comprenant les étapes consistant :
    à échanger (S1) des indicateurs de matrice de précodage (PMI) de matrices de précodage (PM) entre une station de base de cellule d'ancrage (3-0) d'une cellule d'ancrage (2-0) et les stations de base (3-1 à 3-6) de cellules voisines (2-1 à 2-6) ; et
    à prédire (S2), au moyen d'un équipement d'utilisateur (UE) (4), enregistré auprès de la station de base de cellule d'ancrage (3-0) une interférence ICI au niveau de l'équipement d'utilisateur (4), provoquée par les stations de base (3-1 à 3-6) des cellules voisines (2-1 à 2-6), en fonction des indicateurs PMI échangés fournis par la station de base de cellule d'ancrage (3-0) à l'équipement d'utilisateur (4).
  13. Station de base (3-0) d'une cellule d'ancrage (2-0) d'un réseau cellulaire sans fil (1), comprenant une unité d'évaluation qui est conçue pour évaluer une interférence intercellulaire (ICI), l'interférence ICI étant prédite par un équipement d'utilisateur (UE) (4) enregistré auprès de la station de base (3-0), l'interférence ICI au niveau de l'équipement d'utilisateur étant provoquée par des stations de base (3-1 à 3-6) de cellules voisines (2-1 à 2-6), la prédiction étant fonction d'indicateurs de matrice de précodage (PMI) de matrices de précodage (PM), les indicateurs PMI étant fournis par la station de base de cellule d'ancrage (3-0) de la cellule d'ancrage (2-0) à l'équipement d'utilisateur (4) et étant échangés entre la station de base (3-0) de la cellule d'ancrage (2-0) et les stations de base (3-1 à 3-6) des cellules voisines (2-1 à 2-6).
  14. Réseau cellulaire sans fil (1) comprenant des cellules (2-1), chaque cellule comprenant une station de base (3-i), dans lequel des indicateurs de matrice de précodage (PMI) de matrices de précodage (PM) sont échangés entre la station de base de cellule d'ancrage (3-0) d'une cellule d'ancrage (2-0) et les stations de base (3-1 à 3-6) de cellules voisines (2-1 à 2-6) et comprenant également un équipement d'utilisateur (4), enregistré auprès de la station de base de cellule d'ancrage (3-0), l'équipement d'utilisateur étant conçu pour prédire une interférence intercellulaire (ICI) au niveau de l'équipement d'utilisateur (4), provoquée par les stations de base (3-1 à 3-6) des cellules voisines (2-1 à 2-6), en fonction des indicateurs PMI échangés, fournis par la station de base de cellule d'ancrage (3-0) à l'équipement d'utilisateur (4).
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